The World of Coral Reefs
27
Quantifying diversity
Coral
reef diversity is directly comparable to that
of the most diverse terrestrial habitats, the lowland tropical rainforests. At levels of higher taxa
(the more generalized "groups" of species), reefs greatly
outstrip these other mega-diversity ecosystems. Densities
of species per unit-area are also staggering. Species are
often regarded as the building blocks of biodiversity, and,
although reefs occupy only a small area of the planet,
there are probably more species per unit-area of coral
reefs than in any other ecosystem. There are an estimated
4 000 coral reef fish species worldwide, almost a quarter
of all marine fish species. Nearly 1 500 fish species have
been recorded at the Great Barrier Reef in Australia, and
up to 200 species have been recorded from single samples
on individual dives.
Fish represent the dominant vertebrates on coral
reefs, perhaps comparable with the birds of a rainforest,
but their numbers pale into insignificance when compared
with total species composition of reefs. A 5 square meter
reef microcosm sampled in the Caribbean yielded 534
species from 27 phyla, with a further 30 percent of species
not fully identified. One sample of "boring cryptofauna"
(animals which burrow holes and live within the coral
rock) from a single dead coral colony yielded 8 265
individuals from some 220 species. We are only just
beginning to comprehend the scale and depth of this
diversity. Further parallels with tropical rainforests and
other high diversity ecosystems abound.
With this wealth of species a great diversity of
interactions has evolved between species. No organism
lives in isolation, but on reefs the ecological processes
which so oflen drive evolution have pushed the coexistence
of species to extremes. Through pressures such as predation and competition, many species have become highly
specialized to live in tight niches, with highly specific diets,
cryptic habits, or highly evolved defense mechanisms.
Others have become masters of stealth and capture or
camouflage and escape. Co-evolution has also led to
complex two-way interactions between species, including
mutualistic partnerships where both organisms benefit.
The relationship between corals and their algal partners is
perhaps the most important example of such a partnership,
having led to the proliferation and success of the reefbuilding corals.
Like forests, coral reefs also show a considerable
structural diversity, .'\cross the reef zones described above,
but particularly in the areas of most active coral growth, a
coral reef represents a highly complex three dimensional
A dense school of blue-lined snapper Lulianus kasmira, Seychelles.
27
Quantifying diversity
Coral
reef diversity is directly comparable to that
of the most diverse terrestrial habitats, the lowland tropical rainforests. At levels of higher taxa
(the more generalized "groups" of species), reefs greatly
outstrip these other mega-diversity ecosystems. Densities
of species per unit-area are also staggering. Species are
often regarded as the building blocks of biodiversity, and,
although reefs occupy only a small area of the planet,
there are probably more species per unit-area of coral
reefs than in any other ecosystem. There are an estimated
4 000 coral reef fish species worldwide, almost a quarter
of all marine fish species. Nearly 1 500 fish species have
been recorded at the Great Barrier Reef in Australia, and
up to 200 species have been recorded from single samples
on individual dives.
Fish represent the dominant vertebrates on coral
reefs, perhaps comparable with the birds of a rainforest,
but their numbers pale into insignificance when compared
with total species composition of reefs. A 5 square meter
reef microcosm sampled in the Caribbean yielded 534
species from 27 phyla, with a further 30 percent of species
not fully identified. One sample of "boring cryptofauna"
(animals which burrow holes and live within the coral
rock) from a single dead coral colony yielded 8 265
individuals from some 220 species. We are only just
beginning to comprehend the scale and depth of this
diversity. Further parallels with tropical rainforests and
other high diversity ecosystems abound.
With this wealth of species a great diversity of
interactions has evolved between species. No organism
lives in isolation, but on reefs the ecological processes
which so oflen drive evolution have pushed the coexistence
of species to extremes. Through pressures such as predation and competition, many species have become highly
specialized to live in tight niches, with highly specific diets,
cryptic habits, or highly evolved defense mechanisms.
Others have become masters of stealth and capture or
camouflage and escape. Co-evolution has also led to
complex two-way interactions between species, including
mutualistic partnerships where both organisms benefit.
The relationship between corals and their algal partners is
perhaps the most important example of such a partnership,
having led to the proliferation and success of the reefbuilding corals.
Like forests, coral reefs also show a considerable
structural diversity, .'\cross the reef zones described above,
but particularly in the areas of most active coral growth, a
coral reef represents a highly complex three dimensional
A dense school of blue-lined snapper Lulianus kasmira, Seychelles.